This invention relates to the manufacture of pharmaceutical hard gelatin capsules, and particularly to the driving of the capsules during the manufacturing process.
In conventional hard gelatin capsule manufacturing machines, the gelatin solution is continuously gravity-fed from holding tanks into the dipping pans of a Dipper section. The level in the dipping pans is regulated and maintained at a constant level by automatic float valves. These dipping pans are hot-water jacketed and equipped with thermostatically-controlled electric heaters. The gelatin in the dipping pans is maintained at a pre-set temperature by automatic temperature controls to ensure the proper gelatin distribution. Automatic viscosity controls constantly monitor gelatin viscosity and add water to offset evaporation.
The caps and bodies of the capsules are formed on vertically oriented stainless steel mold pins, supported on what are commonly referred to as "pin bars". Each pin bar has stainless steel pins of the size of the desired capsule.
The following is a simplified description of a full cycle through a conventional hard gelatin capsule manufacturing machine.
Two sets (one with the capsule bodies, one with the capsule caps) of pin bars are lowered into the gelatin dipping pan to a level predetermined by a cam (whose size and shape depends on the size of capsules being run on the machine). Once dipped, the pin bars are slowly retracted from the gelatin and elevated to the upper drying kiln.
These two sets of pin bars are then fed into a pair of drying kiln systems each totalling some 50 to 52 feet in running length. In these kilns, the pin bars are subjected to very tightly controlled air conditions. Supply air is controlled to within .+-.1% relative humidity and temperatures of .+-.1.sup.0 Celsius. Liekwise the volume rate of air in cubic feet per minute (cfm) or in cubic metres per hour (m.sup.3 /hr) is also tightly controlled. These close tolerances are essential so that the capsules are not subject to corrugation, brittleness, cracking and so on. If not enough moisture is removed from the capsules during the drying time dictated by the overall speed of the capsule machine, then the capsule halves enter the later operations of the machine in a too wet condition. In this case, further processing (such as stripping the capsule halves from the pin molds, cutting them to the proper lengths, and assembling the two halves to make finished capsules) is impossible. If too much moisture is removed, cracking will result.
The pin bars are first fed by a conveyor system through upper kilns with running lengths of about 26 to 28 feet (depending on the manufacturer of the capsule machine). When the pin bars reach the rear end of the upper kiln, they are pushed onto an elevator. The elevator lowers groups of pin bars into the lower kilns where further drying takes place. After passing through the lower kiln (about 24 feet in length), the drying cycle is complete and the capsules have attained the required moisture content. The pin bars now proceed to the Table section of the machine where they are properly positioned and fed one by one into the Automatic or Finisher section for final operations. This entire drying cycle takes about 36 to 45 minutes depending on the speed at which the capsule machine is being run.
When the pin bars are fed into the Automatic or Finisher section from the Table section, stripper jaws close over the pins and remove the capsule halves. As the capsule halves are being stripped from the pins, collets move forward and receive them. Rods inside the collets position the capsule halves and then the collets move back and lock. The collets then rise and rotate, while cutting knives precisely trim the capsules to the proper length and then withdraw. The trimmings are removed by vacuum in a cutting collector.
The collets containing both caps and bodies move forward and ejector rods push the capsule halves into joiner blocks. At this point the collets retract, leaving the joined capsules in the joiner blocks. The joined capsules are pushed out of the joiner blocks onto a conveyor belt which carries them out of the machine and into a container. Meanwhile, the pin bars move through a Greaser section, in which greaser heads polish the pins and apply a light film of special lubricant. This lubricant facilitates proper stripping of the capsules from the pins on the next cycle.
The pin bars then enter the Dipper section to begin the cycle once more.
The lengthy drying time and the ungainly overall length of the machine has been necessary heretofore due to the inefficient nature of conventional drying which tends to form a skin on the surface of the capsule halves. This makes it very difficult for the moisture within the capsule halves to migrate to the surface and subsequently evaporate as it absorbs heat from the air.
Because the drying cycle is about 38 to 40 minutes in the conventional capsule machine, the machine is about 40 feet in length. A shorter drying cycle would permit the machine to be shortened, which would have obvious cost and other advantages, but hitherto no satisfactory alternative drying means has been developed.